Spoilers & 737NG behaviour

[NicD]

This is great information from eveyone ... thank you all!

I asked the question over on my VA forum. We're an all 737NG VA with many real world Virgin Blue employees - including flight crew. So these guys either jump seat, or crew seat, all the time and know the NG like an old mistress

So ... on the spoiler issue...

The PMDG speedbrake is about as effective as the real thing.. in the -800 she is just too aerodynamic and just doesn't want to slow down when heavy...

Make sure you enter descent winds however .. this makes a big diff to descent calculations especially for e.g. into SYD via CULIN/RIVET8 because of the tailwinds you get on the way down...

And on descent management ...

Many real NG drivers have told me (during descent in the jump seat) that the VNAV PTH does not really hold the descent profile exceptionally well, meaning constat attention and corrections may be necessary. Whilst the profile may be correct, the speed is not. VNAV SPD will hold the speed fairly well on descent but could leave you high or most commonly low on profile.

LVL CH is used frequently, especially in SY. Vert Speed mode used a lot too, allowing manual setting of the speed on the MCP whilst controlling descent to maintain profile (which is displayed on your ND)

No simple answer for a good descent unfortunately. It needs to be assessed constantly and appropriate action taken. I see many pilots in RL, and I myself use a combination to get a good descent and good speeds.

And this advice from a RL 737 skipper:

The 737-800 and the -700 to a lesser extent does have trouble with speed control in VNAV PATH. Its a lot better than it was since Boeing released a software update about 2 years ago, but will still have trouble avoiding an overspeed particularly with a tailwind in excess of about 30 knots.

Its important to note that that - due to the non-linear effect of high altitude descents (too complex to go into here) - that this overspeed generally occurs in the upper third of the descent (say between FL350 and above). Its up high that the barbers pole (MMO or maximum mach number) is perilously close to the typical 0.77M/300kt speed. So, usually once youre established below FL300 you are pretty well home and hosed, with there being a hefty buffer above MMO which climbs to 340 knots.

The idle speeds in flight on descent should see N2 at 59% (ref Boeing manual), with N1 at around 22%. Both figures go up if Anti-Ice is on, and even more when "Approach Idle" kicks in when gear and flaps are out.

I'll try to remember next time i fly to get some video footage of the airspeed runaway during a tailwind descent. I'll try to show the N2/N1 values at the same time.

Finally, remember, VNAV path is putting "Path" as the absolute priority, and this is tricky to achieve in a glide when there are so many variables. VNAV Speed (because it focusses on speed control at the expense of path) does a much better job, but you have to intervene to control divergences from path.

[mauriceb]

Thanks NIC for this extensive 'tutorial'. Lots of very good info there.

One thing I never do actually is enter the winds (descent or other) in the CDU. I always thought the CDU would know what they were since the wind values are displayed on the ND. I actually don't even know where to enter that on the CDU (goes to show my ignorance I guess

Having said that, how would you ever manage to enter the wind value in the CDU when it is constantly changing, especially on the last legs since the headings are changing quite often at that time and you are quite busy in that phase of the flight? Forgetting about VNAV at that time & reverting to manual altitude, speed and V/S control would seem to be the only sensible thing to do then.

By the way, just for fun yesterday, I tried flying the stock Boeing 777 in FS9 in my 737 flight deck. I was amazed at how effective the speed brakes are on that bird and I would actually be shocked if they were that effective on a real 777. It was like I stepped hard on the brakes in my car. The speed dropped dramatically and the rate of descent also increased dramatically. It made me wish I had chosen a 777 instead of a 737.

Thanks,
Maurice

[Michael Carter]

...Forgetting about VNAV at that time & reverting to manual altitude, speed and V/S control would seem to be the only sensible thing to do then....

It's definately the FUN thing to do.

I can't imagine an airplane doing all of the work for me. That's why I learned to fly to begin with because it's FUN!

[Jackpilot]

Way to go...
see my post on TOD...

CDU is fantastic ..but as a tool, not as a pilot.
Has to be your slave not your master.

[mauriceb]

It's definately the FUN thing to do.

I can't imagine an airplane doing all of the work for me. That's why I learned to fly to begin with because it's FUN!

I can't imagine that either, but wouldn't it be nice if everything worked like in a real airplane (within reason of course)?. Aren't we all striving to build something that closely emulates the real thing? If not, why would anyone add a cabin pressure gauge or engine fire extinguisher controls. It's really all a make believe world and the closer it resembles reality, the more enjoyment we get even if we do not really use all the functionality all the time or any time.

I understand what everyone is saying, but I would also bet my next year salary that real Boeing 737 drivers do not have to fight the systems as much as we have to. I want to work at flying & I enjoy real problems & challenges, but not fake ones caused by poor code or flight model or whatever.

And that is what I am talking about & I'm not just trying to be lazy and let the hardware do everything for me, far from it. We already have incredibly complex systems available that we could only dream about only a few years ago and I'm thrilled with what I have. I'm just trying to understand its limitations by finding out if others are experiencing the same problems I have seen.

Anyway, this has been a very good discussion I think and it's nice to be able to do that & get all the different inputs and opinions and this is what makes this forum really good.

Maurice

[Jackpilot]

Way to go too, Maurice....
HEY you are the one who sold me the CDU idea, remember?...and I bought it.
I repeat , it is a wonderful gizmo and like most of us I am far from using all of its potential.

[NicD]

Funny thing is ... Boeing bring out new software for their systems too. New 'builds' just like PM . And when that happens some RL pilots say they are edgy .. unsure of how changes in functionality will perform in the air ... and even worried about bugs. So I guess that feeling we have is a bit like real life. Altho I reckon Boeing do a little more beta testing than PM etc.

[Michael Carter]

I guess that was a small part of why I chose to build an older aircraft. I really don't want the automation the new aircraft provide.

I have an autopilot, very crude by todays standards, but it takes the workload off of me enough so that I can concentrate on navigating and systems monitoring.

And get the occasional Hofbrauhaus from the galley.

[Jackpilot]

"..I guess that was a small part of why I chose to build an older aircraft. I really don't want the automation the new aircraft provide."....

I basically agree with U but even a real Airbus can be flown "sort of" manually.
One has to fight a bit with the systems though.
I was very tempted by the steam gauges of a 737-200 but I must admit that the NG screens get addictive....and the whole beast can be 100% manually handled as long as the flight model is stable,
I use the 800 from Steve Reyling,... really enjoyable to handfly especially on approaches.
PM software used that way is close to perfect as it gives very precise information, like any precision instrument, that the pilot can use as needed.
And the automation can be called upon, on and off, by stages , when the workload is overwhelming, especially with an empty FO seat!

We must not forget that the rationale behind all this automation (CDU mainly)and reduction of crew from 3 to 2 is SAVINGS and Fuel Economy, far before safety....modern airliners are now always driven in a boring "economy mode" .
We do not have to abide by those rules.

Well, whatever the methods...this is a GREAT HOBBY, and as Maurice said, a great way to share ideas...
Have a good one Guys.